Stop off wrap

ABSTRACT

A method of applying a coating to a tubular by covering a portion of the outer surface of the tubular with a wrapping material, coating the tubular, and removing the wrapping material.

TECHNICAL FIELD

Method and apparatus for stopping off a tubular.

BACKGROUND

It is known in the oil and gas industry to coat metal equipment in metal alloy coatings. A significant percentage of these tubulars only require coatings on particular portions of the tubular, often only on the inner diameter surface and a threaded portion of the outer diameter surface. Coating the non-threaded exterior portions of these tubulars would results in substantially higher chemical and labor costs. It is desirable to stop off these portions of the tubulars to prevent the coating from being applied. Complicating this task is the high temperature of the process bath (typically ˜190° F.), the highly alkaline pretreatment steps, and the sensitivity of the process chemistry to any dragged in contaminants. Many of the tubulars to be processed have substantial rust, paint and other soils on the outside that cannot be allowed to contaminate the large and costly autocatalytic nickel bath.

The industry standard for stopping off parts for autocatalytic nickel plating has been to use solvent based rubberized stop off paints such as Enplate Stop-Off No. 1 (supplied by Enthone, West Haven, Conn., USA) or Coverlac A-2114 Maskant (supplied by Spraylat Corporation, Mount Vernon, N.Y., USA). These products can be applied by brush or spray equipment and use xylene or toluene as thinner. Unlike many other stop off paints these products remain bonded even through long term exposure to 190° F. bath chemistry when applied to a clean surface. They are marketed as peelable but this often takes a great deal of effort or the use of solvents particularly on a blasted surface. If used on the tubular outer diameter surface, a pre-cleaning and oxide removal would be required. A substantial drying period is required after application and multiple coats would be needed if sprayed. The large surface area to be stopped off, the VOC and flammability issues of these products, and excessive time needed to apply and remove the stop off make this method undesirable for this application and prompt a desire for an alternative stop off method.

SUMMARY

In an embodiment there is disclosed a method of applying coating a tubular having an outer surface and an inner surface, comprising covering a selected portion of the outer surface of the tubular with wrapping material by wrapping the wrapping material around the tubular in a spiral having succeeding flights, with overlapping portions between succeeding flights of the spiral, wherein the wrapping material has a softening point, providing coating material, wherein the coating material has a temperature above the softening point of the wrapping material, applying the coating material to the tubular and to the wrapping material and thereby causing the wrapping material to soften and self-adhere at the overlapping portions; and removing the wrapping material from the tubular.

In various embodiments, there may be included any one or more of the following features: the coating may be applied to the tubular in a chemical bath, the wrapping material may substantially prevent coating fluid from being applied to the covered portion of the outer surface of the tubular, the coating may be applied by electroplating, the coating may be applied by electroless plating, electroless plating may be electroless nickel plating, the wrapping material may be substantially non-conductive, the wrapping material may be a polymer, the polymer may be one or more LDPE (low density polytheylene), EVA (ethylene vinyl acetate), PVdC (polyvinylidene chloride), LLDPE (linear low-density polyethylene), PVC (polyvinylchloride), metallocene treated LLDPE, and metallocene treated polyethylene, the wrapping material may be secured to the tubular at its ends by an adhesive tape, the adhesive tape may be electroplating tape, the tubular may have one or more threaded ends with the wrapping material not covering the one or more threaded ends.

These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:

FIG. 1 is a side-view of a tubular.

FIG. 2 is a side-view of a partially wrapped tubular.

FIG. 3 is a side-view of a fully wrapped tubular.

FIG. 4 is a side-view of a wrapped tubular in which the wrapping has been secured.

FIG. 5 is a side-view of a wrapped tubular submerged in a chemical bath.

DETAILED DESCRIPTION

Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.

Referring to FIG. 1-3, there is shown a tubular 10 having an outer surface 12 and inner surface 22. The tubular 10 can additionally have one or more threaded ends 14. A selected portion of the outer surface of the tubular 10 is wrapped in a wrapping material 16 to cover a selected portion of the outer surface of the tubular 10 with wrapping material 16. The wrapping material 16 is wrapped around the tubular 10 in a spiral having succeeding flights, with overlapping portions between succeeding flights of the spiral. In an embodiment, the wrapping material 16 may be wrapped multiple times over each covered portion of the exterior of the tubular, for example forming 2, 3, 4 or more layers, each of which completely covers the tubular exterior between the threads.

The selected portion would generally be the portion of the outer surface of the tubular 10 that does not require application of the coating. In most cases the portion selected would be the portion of the outer surface of the tubular 10 that is not threaded. In some embodiments the wrapping material 16 may be sheets of a polymer such as linear low-density polyethylene. In another embodiment the wrapping material 16 may be a polymer film or adhesive backed film having suitable softening and melting temperatures as discussed herein. The wrapping material 16 may be wrapped by hand or the wrapping may be automated by using any one of a number of wrapping machines that are commercially available. The wrapping material 16 may be wrapped spirally in an overlapping fashion. In the figures the lines on the wrapping material show the flights of the spiral. The degree of overlap in the flights of the spiral could vary between tubulars or over the course of a single tubular 10 and in some cases there could be three or more layers of overlapping material. The wrapping material 16 should be held at a level of tension during wrapping to ensure that the wrapped surface is effectively fluid-tight. In a typical embodiment threaded ends of the tubular 10 are not covered with wrapping material 16. The wrapping material 16 should be sufficiently stretchable, pliable and flexible to be applied to the outside of the tubing while rotating and create a seal. In some cases, the wrapping material 16 should be sufficiently flexible to follow uneven surfaces such as dirty or worn tubulars and still form a seal at overlapping portions that self-adheres in a chemical bath.

Once the wrapping material 16 has been wound onto the tubular 10, a coating material may be applied to the tubular 10 and to the wrapping material 16, for example by dipping the tubular 10 in a bath of coating material 20. The wrapping material 16 should be able to handle temperatures of 190 F plus (88 C) or such other temperature that the bath is set to and be chemically inert to the bath fluid, but have a softening point below the temperature of the coating material 20, and a melting point that is above the temperature of the coating material 20. Thus when the coating material 20 contacts the wrapping material 16, the wrapping material 16 softens and self-adheres at overlapping portions. The wrapping material 16 should bond (adhere) to itself with sufficient adhesion in a manner that prevents any leaking of bath fluid through the wrapping material 16 after being wrapped around the tubular 10. For the example of low density polyethylene used as the wrapping material 16, the softening point is about 80 C and the melting point is about 105 C, which is suitable for a typical coating material bath at 88 C. It may be preferable that the coating temperature be closer to the softening point of the wrapping material 16 than to the melting point of the wrapping material. Applying the coating material 20 to the tubular 10 and to the wrapping material 16 and causes the wrapping material 16 to soften and self-adhere at the overlapping portions.

If low-density polyethylene is used as a wrapping material 16, securing material 18 may then be used to secure the wrapping material 16 to the tubular 10 (see FIG. 4). In other embodiments the securing material may be metal bands, metal wire or high temperature zip-ties. The metal bands or metal wire may be tied around a circumference of the tubular at each end of the wrapped portion. The metal bands or wire are preferably tied sufficiently tightly to ensure a fluid-tight seal between the wrapping material and the tubular at each end of the wrapped portion. If the wrapping material 16 is suitably stretched around the tubular and sufficiently flexible and tight or if adhesive tape is used then securing material 18 may not be necessary if the wrapping material adheres directly to the tubular 10. The ends may in some cases be secured to the tubular with tape such as electroplating tape.

Once the tubular 10 has been wrapped in a suitable wrapping material 16 a coating is then applied to the tubular. The coating is applied at a temperature above the softening point of the wrapping material so that at overlapping portions of the wrapping material, the wrapping material self-adheres (fuses) to provide a seal against coating material 20 contacting the wrapped portion of the tubular. The coating may be applied in a bath of coating material 20, as shown in FIG. 5, potentially using electroplating or electroless plating. When using electroplating and electroless plating it is desirable that the wrapping material be non-conductive to prevent unnecessary waste of the coating material 20. In an embodiment the coating is applied using electroless nickel plating. For some wrapping materials, such as linear low-density polyethylene, the heat of the chemical bath cause overlapping segments of the wrapping material to fuse together, further improving the fluid-tight seal. After the application of the coating, the wrapping material 16 is removed from the tubular 10. Depending on the material used, the wrapping material 16 may be unwrapped or cut from the tubular 10.

Materials that may be used for the wrapping material include LDPE (low density polytheylene), EVA (ethylene vinyl acetate), PVdC (polyvinylidene chloride), LLDPE (linear low-density polyethylene), PVC (polyvinylchloride), metallocene treated LLDPE, and metallocene treated polyethylene. Other types of polyethylene and PVC (particularly PVdC) polymers can also be used. To obtain improved two sided adhesion (cling) of the stretch wrap to itself polyisobutene (PIB) and poly[ethylene-vinylacetate] copolymer are added to LLDPE or PVdC.

Stretch wrap is broken down into two types depending on how it is manufactured and either may be used if the material otherwise has suitable melting and softening points. Cast stretch wrap is manufactured using a cast extrusion process. The Cast extrusion process is a continuous process by which a thermoplastic material is melted and extruded through a flat die onto a chill roll, where it is quenched and re-solidified. This process allows the Cast stretch film to have excellent clarity, require less force to stretch, increased tear resistance, unwind quietly from machines, and offer a superior cling. There are both machine grade and hand grade cast stretch film available. Cast Stretch Film is generally less expensive than blown stretch film, due to reduced manufacturing costs. Increased clarity allows users to see wrapped products. Cast stretch wrap unwinds quietly compared to blown stretch wrap. Cast stretch wrap offers two sided cling that allows the wrap to stay securely wrapped. On the other hand, cast stretch wrap does not offer the load/holding power blown stretch film offers. Cast stretch film has less memory and tear resistance than blown stretch film.

Blown stretch wrap is manufactured using the blown extrusion process. This Plastic melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. On top of the tube an air ring blows onto the film to cool it. This process allows blown film to be tougher and more resilient than cast film. The higher mechanical properties of blown film typically allow a greater load holding power. Blown stretch wrap offers higher load and stretch capacity. Blown stretch wrap is a higher quality of film. Blown stretch wrap has a higher degree of memory once stretched allowing loads to stay better secured. A higher tear resistance is an advantage when securing loads with sharp edges. Blown stretch wrap has higher cost due to manufacturing process. Blown stretch wrap has poor clarity due to crystallisation in the manufacturing process. Blown film is also noisy when unwound from rolls. 

1. A method of applying coating a tubular having an outer surface and an inner surface, comprising: covering a selected portion of the outer surface of the tubular with wrapping material by wrapping the wrapping material around the tubular in a spiral having succeeding flights, with overlapping portions between succeeding flights of the spiral, wherein the wrapping material has a softening point and a melting point; providing coating material, wherein the coating material has a temperature above the softening point of the wrapping material and below the melting point of the wrapping material; applying the coating material to the tubular and to the wrapping material and thereby causing the wrapping material to soften and self-adhere at the overlapping portions; and removing the wrapping material from the tubular.
 2. The method of claim 1 in which the coating material is applied to the tubular in a chemical bath.
 3. The method of claim 1 in which the wrapping material is substantially non-conductive and the coating material is applied by electroplating.
 4. The method of claim 1 in which the wrapping material comprises a polymer.
 5. The method of claim 4 in which the polymer comprises one or more of LDPE (low density polytheylene), EVA (ethylene vinyl acetate), PVdC (polyvinylidene chloride), LLDPE (linear low-density polyethylene), PVC (polyvinylchloride), metallocene treated LLDPE, and metallocene treated polyethylene.
 6. The method of claim 1 in which, after wrapping the wrapping material on the tubular, the wrapping material has ends, and the method further comprising securing the ends of the wrapping material to the tubular.
 7. The method of claim 1 in which the tubular has threaded ends and the wrapping material does not cover the threaded ends. 